The overall goal of the research proposed in this application is to understand the molecular basis of cardiac arrhythmias caused, at least in part, by inherited mutations of the SCN5A gene, and to determine novel gene-targeted therapeutic strategies to treat them. The central hypothesis is that one step in the genesis of these arrhythmias is the perturbation of membrane electrical activity caused by alteration in the biophysical properties of the SCN5A gene product, the principal cardiac Na+ channel alpha subunit, by diseased-linked mutations, but that similar functional perturbations may be linked to distinct clinical disorders. Altered ion channel properties may also confer unique pharmacological properties upon the encoded ion channels making them unique targets for therapeutic intervention but, perhaps less effective in unmasking distinct inherited syndromes. We will focus on identified SCN5A mutations linked to the long QT syndrome (LQT-3) and Brudaga's syndrome (BrS) as paradigms to test this hypothesis. Structural analysis of the alpha subunit and site directed mutagenesis will complement the analysis of inherited mutations to provide a structural framework to interpret alteration in channel function. There are two aims of this project. Aim 1 is to test the hypothesis that there can be functional overlap caused by inherited mutations of the SCN5A gene linked either to BrS or LQT-3. Aim 2 is to test the hypothesis that there can be overlap in inherited BrS and LQT-3 SCN5A mutation-specific pharmacology due to overlap in mutation induced gating changes of expressed channels. Experiments that are proposed will combine patch clamp measurement of recombinant channel activity transiently expressed in mammalian cells. Theoretical testing of our predictions will be carried out using computer-based simulations of ion channel gating and cardiac action potentials that incorporate our patch clamp data. We hypothesize that information gained from these cellular and molecular experiments can be translated directly to improved therapeutic intervention in humans based on specific properties of mutant gene products, and also shed light on the possible interrelationship of these two inherited disorders.